Error "AdbCommandRejectedException: device not found" in Eclipse using Android emulator

I've tried to change the build of an application, and now eclipse doesn't work.

There is nothing in the console, and when I launch the debug, there is nothing on the log.

I just got this message :

[2011-03-31 11:22:58 - Logcat]device not found
com.android.ddmlib.AdbCommandRejectedException: device not found
at com.android.ddmlib.AdbHelper.setDevice(AdbHelper.java:736)
at com.android.ddmlib.AdbHelper.executeRemoteCommand(AdbHelper.java:373)
at com.android.ddmlib.Device.executeShellCommand(Device.java:284)
at com.android.ddmuilib.logcat.LogPanel$3.run(LogPanel.java:527)